1. Field of the Invention
This invention relates to pipe swivel joints, and more particularly, to such swivel joints for use at underwater or other submerged locations.
2. Description of the Prior Art
Pipe swivel joints are commonly used by the oil and gas industry for interconnecting lengths of metal pipe to form an articulated flow conduit between two locations. One of the more modern of such uses is in a product flowline extending between a subsea station on the ocean floor and a buoy or other surface floating facility: for example, an offshore mooring and loading terminal for marine tankers. Swivel joints employed for this purpose are subjected to constant motion, to a corrosive environment, and to relatively high external hydrostatic pressures, and it is imperative that they do not leak either outwardly, thereby polluting the ocean environment, or inwardly and thus contaminate the product in the flowline. Prior to the present invention, a maintenance program involving removal and/or repair of these submerged swivel joints has been necessary to prevent leaks from occurring, and such a program has proved to be both inconvenient and costly.
Rubber or other relatively flexible hose, the obvious alternative to an all-metal articulated flowline, has its own serious drawbacks. It is difficult to construct a large diameter hose for submerged service that will not burst when subjected to brief high pressure surges in the product system, and will not collapse when the product system pressure drops to zero. Furthermore, hoses that will withstand these wide pressure conditions are quite large, inflexible, and difficult to handle, and leakage through this type of hose is likely to occur in a sudden, massive and otherwise dramatic manner that presents little if any possibility of monitoring or minimizing the problem.
It is desirable to provide a product flowline having rigid pipes with swivel joints which can be checked for leaks on a continuing basis without removal of the joints. It is also desirable that a detected leak can be temporarily stopped by remote control without an interruption of the flow of the product through the flowline.